Preparation Of Dual Phase Ceramic Hollow Fiber Membranes And Application In NH₃ Decomposition For Hydrogen Production

Perovskite-based mixed conductor membranes can be used in various aspects including hydrogen involved reactors due to their characteristics of proton conductivity.While the hydrogen permeability is limited by the factor of lower electronic conductivity.In order to solve the poor conductivity of the membrane,we developed a dual-phase ceramic membrane.In this work,SrCe_0.9Y_0.1O₃-δ（SCY）was chosen as the fundamental proton conductor.The new phases（Ce）SrTiO₃ and（Y）CeO₂ which were formed due to the solid state reaction between Ti₄O₇ and SCY can be served as electron conductor.The ceramic dual phase hollow fiber membranes were fabricated via the method of phase inversion and solid phase reaction.The compositions,crystal structures,microstructures and properties of the hollow fiber membrane were investigated by XRD,SEM and GC tests.The results show that the solid reaction between Ti₄O₇ and SCY occurred at 900 oC and the new phases（Ce）SrTiO₃ and（Y）CeO₂ were created along the grain boundaries and restrained the growth of SCY grains during the sintering process.The 5 wt% was the optimized doping mass ratio from the results of conductivity and permeability tests,in the values of which were 0.038 S·cm^-1 in the hydrogen content atmosphere and 0.17 mL·min^-1·cm^-2 at 900 oC using N₂ as sweep gas,respectively.The hydrogen permeation flux is well described by a power-law relationship with the hydrogen partial pressure gradient across two sides of membrane.The reverse water-gas shift reaction can enhance the permeation flux of the membranes.The hydrogen permeation flux reached 0.57 mL·min^-1·cm^-2 at 900 oC with 9.5 vol% CO₂ in sweep gas side.Through detailed investigation on the catalytic properties of the hollow fiber membrane materials and reactors for the reverse water gas shift reaction,it was found that the promotion of hydrogen permeability caused by the reverse water gas shift reaction can be mainly attributed to the strong adsorption ability of membrane materials to CO₂ and the SCY makes a major contribution to the CO₂-adsorption.The oxygen vacancies in SCY offer the main active sites for CO₂ reducing.The reaction between H2 and CO₂ promote the bulk diffusion and surface reaction rates of protons.The properties of the dual phase membrane materials catalyzing ammonia decomposition were investigated.The results show that the good performance of the hollow fiber membrane was confirmed in the process of ammonia decomposition.The conversion rate of 92.7% was obtained in the packed bed reactor at 900 oC using 20% NH₃ as feed gas.The NH₃ conversion of 51.9% and hydrogen separation efficiency of 1.28% were obtained at 900 oC in the catalytic membrane reactor coated with the membrane materials as catalysis,using 20% NH₃ as feed gas.